Prognostic Meteorological Discussion
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FXAK02 KWNH 192011
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
410 PM EDT WED JUL 19 2017

VALID 12Z SUN JUL 23 2017 - 12Z THU JUL 27 2017

THE MAIN FEATURE GOVERNING THE WEATHER PATTERN THIS WEEKEND AND
GOING INTO NEXT WEEK WILL BE A LARGE HIGH PRESSURE RIDGE AT BOTH
THE SURFACE AND ALOFT OVER THE ALEUTIANS AND SOUTHERN BERING SEA.
THIS IS FORECAST TO REACH ITS MAXIMUM STRENGTH ON TUESDAY AND
WEDNESDAY WITH SOME OF THE DETERMINISTIC SOLUTIONS INDICATING A
594DM CONTOUR, WHICH IS IMPRESSIVE FOR A HIGH AT THIS LATITUDE.
NEVERTHELESS, THE WPC FORECAST INCLUDED IT ON THE 500MB PROGS
GIVEN MULTIPLE MODEL RUNS INDICATING IT.  THIS WILL RESULT IN
SHORTWAVE PERTURBATIONS TRAVERSING THE NORTHERN PERIPHERY OF THE
RIDGE WITH A GENERAL TROUGH BECOMING ESTABLISHED OVER THE GULF OF
ALASKA.  NOTHING PARTICULARLY STRONG IN TERMS OF LOW PRESSURE
SYSTEMS WERE NOTED IN THE GUIDANCE, SO THE WPC PROGS FEATURE A FEW
MODEST SURFACE LOWS TO THE NORTH AND EAST OF THE RIDGE.  THE
GREATEST UNCERTAINTY EXISTS WITH THE FASTER FLOW PATTERN NEAR THE
ARCTIC COAST WITH MULTIPLE SPEED AND LATITUDE DIFFERENCES IN THE
GUIDANCE WITH RESPECT TO INDIVIDUAL SHORTWAVE FEATURES.
THEREFORE, A NEARLY EQUAL BLEND OF THE OPERATIONAL GFS AND ECMWF,
ALONG WITH INCREASING PERCENTAGES OF THEIR RESPECTIVE MEANS GOING
FORWARD IN TIME, WAS USED IN THE FORECAST.

THE WARMEST DAY DURING THIS PERIOD WILL LIKELY BE ON SUNDAY WITH
SOME LOWER TO MID 70S FOR HIGHS ACROSS PORTIONS OF THE CENTRAL AND
SOUTHERN INTERIOR REGION.  A GRADUAL COOLING TREND SHOULD COMMENCE
GOING INTO THE BEGINNING OF THE WEEK.  SCATTERED SHOWERS AND A FEW
THUNDERSTORMS ARE LIKELY ACROSS THE INTERIOR AND ALSO FOR THE
EASTERN PANHANDLE REGION.  THE ALEUTIANS SHOULD REMAIN DRY WITH
THE LARGE HIGH PRESSURE RIDGE IN PLACE.

HAMRICK

$$




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